Prevalence, diversity and risk factors of gastrointestinal parasites in dogs housed at official shelters across Portugal

Gastrointestinal parasites (GIP) are among the most common pathogens that affect dogs globally, with some species representing a zoonotic threat. Stray and shelter dogs are especially vulnerable to parasitism as their clinical history is often unknown, and copro-parasitological analyses are seldom performed upon animal arrival at shelters. In Portugal, official shelters play a pivotal role in sheltering and managing stray dogs; however, little is known about the GIP infection status of these animals. This study thus aimed to determine the occurrence of GIP in dogs housed at official shelters in Portugal and explore potential variables contributing to the GIP burden. Between November 2021 and October 2022, a total of 355 dog faecal samples were collected from shelters across the country. These samples were either obtained individually from dogs or pooled from groups of animals housed together, and were analysed using the Mini-FLOTAC technique with zinc sulphate flotation solution (specific gravity 1.35) to detect, identify, and quantify GIP shedding intensity. Over 16 % (57/355) of the samples were GIP-positive. The most frequently observed parasites were Trichuris vulpis (20/355), Toxocara canis (19/355), Ancylostoma spp. (13/355), and Cystoisospora canis (8/355). Co-infections with two parasitic agents were detected in three individual samples: two dogs harboured both T. vulpis and C. canis, while one dog was co-infected with T. vulpis and T. canis. Most positive samples (53/59) exhibited a moderate to high shedding intensity, with over 50 eggs or oocysts per gram of faeces - EPG or OPG, respectively. Only a few showed a low shedding intensity of less than 10 EPG or OPG. When examining individual faecal samples, the average prevalence rate of GIP in shelter dogs across sampled regions was 15.9 % (33/208). A single taeniid infection was detected and confirmed, via molecular assays, to be due to Echinococcus granulosus. The occurrence of Ancylostoma spp. and T. vulpis were significantly correlated with the number of dogs housed in shelters. The presence of Ancylostoma spp. eggs was significantly associated with season and region, while consistency of faeces was significantly associated with the presence of T. canis eggs and GIP co-infection status. This study represents the first nationwide screening for GIP in shelter dogs in Portugal. Our findings underscore the importance of regular screening in shelters, namely upon animals' arrival, and the need for active, effective management of infections to control GIP spread within the shelter and to prevent possible occupational zoonotic transmission.